Electrochromic devices having improved ion conducting layers

ABSTRACT

An improved ion conductor layer for use in electrochromic devices and other applications is disclosed. The improved ion-conductor layer is comprised of at least two ion transport layers and a buffer layer, wherein the at least two ion transport layers and the buffer layer alternate within the ion conductor layer such that the ion transport layers are in communication with a first and a second electrode. Electrochromic devices utilizing such an improved ion conductor layer color more deeply by virtue of the increased voltage developed across the ion conductor layer prior to electronic breakdown while reducing the amount of electronic leakage. Also disclosed are methods of making electrochromic devices incorporating the improved ion conductor layer disclosed herein and methods of making ion conductors for use in other applications.

This application claims the benefit of the filing date of U.S.Provisional Patent Application No. 60/725,581 filed Oct. 11, 2005, thedisclosure of which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to electrochromic devices and moreparticularly relates to solid-state, inorganic thin film electrochromicdevices.

Electrochromic materials and devices have been developed as analternative to passive coating materials for light and heat managementin building and vehicle windows. In contrast to passive coatingmaterials, electrochromic devices employ materials capable of reversiblyaltering their optical properties following electrochemical oxidationand reduction in response to an applied potential. The opticalmodulation is the result of the simultaneous insertion and extraction ofelectrons and charge compensating ions in the electrochemical materiallattice.

In general, electrochromic devices have a composite structure throughwhich the transmittance of light can be modulated. FIG. 1 illustrates atypical five layer solid-state electrochromic device in cross-sectionhaving the five following superimposed layers: an electrochromicelectrode layer (“EC”) 14 which produces a change in absorption orreflection upon oxidation or reduction; an ion conductor layer (“IC”) 13which functionally replaces an electrolyte, allowing the passage of ionswhile blocking electronic current; a counter electrode layer (“CE”) 12which serves as a storage layer for ions when the device is in thebleached or clear state; and two conductive layers (“CL”) 11 and 15which serve to apply an electrical potential to the electrochromicdevice. Each of the aforementioned layers are typically appliedsequentially on a substrate 16. Such devices typically suffer fromelectronic leakage and electronic breakdown.

In order for a solid state electrochromic device to function correctly,it is necessary to incorporate an ion conductor layer which effectivelyblocks electronic current while admitting the passage of ions (typicallyprotons (H⁺) or lithium ions (Li⁺)) at a reasonable rate. However, anyelectronic current that leaks or passes through the ion conductor layerserves to short out the required voltage and inhibits the flow of ions.As such, electronic leakage current leads to compromises in deviceperformance including a lowered dynamic range, non-uniform coloration,decreased ionic conductance, slower switching rates, and increased powerconsumption. Merely increasing the thickness of the ion conductor layermay result in a reduction of leakage current, but at the expense ofdegraded optical properties, increased layer deposition time and cost,and reduced switching rates. Accordingly, it is desirable to reduce theamount of electronic leakage through an electrochromic device withoutresorting to a thick ion conductor layer so as to avoid thesecompromises in performance.

Moreover, solid state electrochromic devices are also subject to“electronic breakdown.” FIG. 2 shows the equilibrium electrical andoptical characteristics of an electrochromic device for applied voltagesin the ‘forward’ or coloring polarity, up until the point wheresubstantial electronic leakage current begins to flow. Thesecharacteristics are plotted as a function of the internal voltage, whichis the voltage applied to the device minus the voltage induced in theseries resistance as a result of the current flowing. Initially, thereis a slow increase in the current density below a particular ‘thresholdvoltage,’ accompanied by an increase in optical density. Above thethreshold voltage, however, the electrochromic device breaks downelectronically and any additional current flowing is primarilyelectronic leakage. Moreover, reaching the threshold voltage preventsany further increases in voltage across the electrochromic device. Sincethe coloration of a device is related to the voltage that can bedeveloped across the electrochromic device, the threshold voltage willdetermine the maximum obtainable optical density for a given devicestructure, i.e. a particular layer thickness, and, hence its dynamicrange. As such, it is desirable to increase the voltage that can bedeveloped across the ion conductor layer of the electrochromic deviceprior to it breaking down so as to allow electrochromic devices to colormore deeply and to reduce power consumption.

Takahashi (U.S. Pat. No. 4,293,194) discloses a device having decreasedelectronic leakage. Takahashi teaches a solid electrochromic deviceincorporating an electron blocking material comprised of a layer of anN-type semiconductor adjacent to a layer of a P-type semiconductor.However, Takahashi does not teach a multi-layered thin film ionconductor layer capable of reducing electronic leakage while increasingthe voltage that may be developed across the ion conductor layer.

SUMMARY OF THE INVENTION

In accordance with the present invention, an electrochromic device hasbeen discovered comprising a first electrode comprising one of anelectrochromic electrode layer and a counter electrode layer, a secondelectrode comprising the other of said electrochromic electrode layerand said counter electrode layer, an ion-conductor layer for conductingions between the first and second electrodes comprising at least two iontransport layers and a buffer layer, the at least two ion transportlayers and the buffer layer alternating within the ion conductor layersuch that the ion transport layers are in communication with the firstand second electrodes, a first conductive layer, and a second conductivelayer, wherein the first and second electrodes and the ion-conductorlayer are sandwiched between the first and second conductive layers.

In accordance with one embodiment of the present invention, adjacentones of the at least two ion transport layers and buffer layer arecomprised of different materials.

In accordance with another embodiment of the present invention, the atleast two ion transport layers are comprised of an insulator. In someembodiments, the insulator is comprised of a material selected from thegroup consisting of silicon oxides, aluminum oxides, aluminum nitrides,niobium oxides, tantalum oxides, zirconium oxides, yttrium oxides,hafnium oxides, and mixtures thereof. In other embodiments, theinsulator is comprised of a material selected from the group consistingof SiO₂, Al₂O₃, Nb₂O₃, Ta₂O₅, LiTaO₃, LiNbO₃, La₂TiO₇, La₂TiO₇, SrZrO₃,ZrO₂, Y₂O₃, Nb₂O₅, La₂Ti₂O₇, LaTiO₃, HfO₂, and mixtures thereof.

In accordance with another embodiment of the present invention, theinsulator is a mixture of a silicon oxide and an aluminum oxide, whereinan amount of the silicon oxide to an amount of the aluminum oxide rangesfrom about 25:1 to about 1:25, preferably ranging from about 11:1 toabout 17:1.

In accordance with another embodiment of the present invention, theinsulator is a mixture of a zirconium oxide and a yttrium oxide, whereinan amount of the zirconium oxide to an amount of the yttrium oxideranges from about 25:1 to about 1:25.

In accordance with another embodiment of the present invention, the atleast two ion transport layers have a thickness ranging from about 1 nmto about 70 nm, preferably from about 5 nm to about 30 nm.

In accordance with another embodiment of the present invention, thematerial comprising the buffer layer is selected from the groupconsisting of transparent lithium ion permeable materials and mixedconductors. In some embodiments of the present invention, the materialcomprising the buffer layer is selected from the group consisting oftungsten oxides, nickel oxides, cerium oxides, molybdenum oxides,vanadium oxides, and mixtures thereof. In other embodiments of thepresent invention, the buffer layer is comprised of a material selectedfrom the group consisting of WO₃, NiO, CeO₂, MoO₃, V₂O₅, and mixturesthereof. In yet other embodiments, the buffer layer is comprised of alithium-based ceramic material including lithium silicates, lithiumaluminum silicates, lithium aluminum borates, lithium borates, lithiumsilicon oxynitrides, lithium zirconium silicates, lithium niobates,lithium borosilicates, lithium phosphosilicates, lithium nitrides,lithium aluminum fluoride, and mixtures thereof.

In accordance with another embodiment of the present invention, thebuffer layer has a thickness ranging from about 10 nm to about 300 nm,preferably from about 30 nm to about 150 nm.

In accordance with another embodiment of the present invention, theelectrochromic electrode layer is comprised of a material selected fromthe group consisting of metal oxides and mixed metal oxides includingtungsten oxides, vanadium oxides, molybdenum oxides, niobium oxides,titanium oxides, copper oxides, iridium oxides, chromium oxides, cobaltoxides, manganese oxides, and mixtures thereof.

In accordance with another embodiment of the present invention, thecounter electrode layer is comprised of a material selected from thegroup consisting of metal oxides and mixed metal oxides includingvanadium oxides, niobium oxides, nickel oxides, nickel hydroxides,iridium oxides, copper oxides, tungsten oxides, molybdenum oxides, andmixtures thereof. In some embodiments, the mixed metal oxides comprise afirst transition metal oxide present as a stable metal oxide matrix anda second transition metal doped into the stable metal oxide matrix. Inpreferred embodiments, the first transition metal oxide is selected fromthe group consisting of chromium, tungsten, and tantalum, and the secondtransition metal oxide is selected from the group consisting of vanadiumand nickel.

In accordance with another embodiment of the present invention, thefirst and second conductive layers are comprised of a material selectedfrom the group consisting of metal oxides and transparent coatings oftransition metals.

In accordance with another embodiment of the present invention, theelectrochromic device is disposed on a substrate selected from the groupconsisting of glass and plastic.

In accordance with another objective of the present invention, an ionconductor layer for transporting ions between a first electrode and asecond electrode comprising at least two ion transport layers and abuffer layer has been discovered, wherein the at least two ion transportlayers and the buffer layers alternate within the ion conductor layersuch that the ion transport layers are in communication with the firstand second electrodes.

In accordance with one embodiment of the present invention, adjacentones of the at least two ion transport layers and buffer layer arecomprised of different materials.

In accordance with another embodiment of the present invention, the atleast two ion transport layers are comprised of an insulator includingsilicon oxides, aluminum oxides, aluminum nitrides, niobium oxides,tantalum oxides, zirconium oxides, yttrium oxides, hafnium oxides, andmixtures thereof.

In accordance with another embodiment of the present invention, thebuffer layer is selected from the group consisting of transparentlithium ion permeable materials and mixed conductors. In someembodiments of the present invention, the buffer layer is selected fromthe group consisting of tungsten oxides, nickel oxides, cerium oxides,molybdenum oxides, vanadium oxides, and mixtures thereof. In otherembodiments, the buffer layer is comprised of lithium-based ceramicmaterials.

In accordance with the present invention, a method for the preparationof an electrochromic device has been discovered comprising the followingsteps: a) providing a first conductive layer, b) depositing one of anelectrochromic electrode layer and a counter electrode layer on thefirst conductive layer, thereby providing a first deposited electrode,c) depositing an ion-conductor layer on the first deposited electrode,the ion-conductor layer comprising at least two ion transport layers anda buffer layer, wherein the at least two ion transport layers and thebuffer layer are sequentially applied such that one of the at least twoion transport layers is in communication with the first depositedelectrode, d) depositing the other of the electrochromic electrode layerand the counter electrode layer on the ion-conductor layer, therebyproviding a second deposited electrode in communication with the otherof the at least two ion transport layers, and e) depositing a secondconductive layer on the second deposited electrode.

In accordance with another embodiment of the method of the presentinvention, the method includes subsequently subjecting at least one ofthe first and second deposited electrodes to a heat treatment step,whereby the heat treatment step may be in a vacuum, an inert atmosphere,or an atmospheric oven. The heat treatment step may be performed at atemperature ranging from about 40° C. to about 550° C., preferablyranging from about 200° C. to about 500° C.

In accordance with another embodiment of the method of the presentinvention, the method comprises independently depositing the firstand/or second electrodes by means of a method selected from the groupconsisting of physical vapor deposition, intermediate frequency reactivesputtering, DC sputtering, and wet chemical methods.

In accordance with another embodiment of the method of the presentinvention, the method includes reducing at least one of the first andsecond deposited electrodes by inserting ions thereinto. In someembodiments, the reducing step is effected during the depositing of thefirst and second electrodes. The inserted ions may be selected from thegroup consisting of lithium ions, sodium ions, and protons.

In accordance with another embodiment of the method of the presentinvention, the method comprises independently depositing the iontransport layers by means of a method selected from the group consistingof physical vapor deposition, intermediate frequency reactivesputtering, DC sputtering, wet chemical methods, laser ablation methods,sol-gel, metallo-organic decomposition, and magnetic sputtering.

In accordance with another embodiment of the method of the presentinvention, the method comprises depositing the buffer layer by means ofa method selected from the group consisting of physical vapordeposition, intermediate frequency reactive sputtering, DC sputtering,wet chemical methods, laser ablation methods, sol-gel, metallo-organicdecomposition, and magnetic sputtering.

In accordance with another embodiment of the method of the presentinvention, adjacent ones of the at least two ion transport layers andbuffer layer are comprised of different materials.

In accordance with another embodiment of the method of the presentinvention, the at least two ion transport layers are comprised of aninsulator. In some embodiments, the insulator is comprised of a materialselected from the group consisting of silicon oxides, aluminum oxides,aluminum nitrides, niobium oxides, tantalum oxides, zirconium oxides,yttrium oxides, hafnium oxides, and mixtures thereof. In otherembodiments, the insulator is comprised of a material selected from thegroup consisting of SiO₂, Al₂O₃, Nb₂O₃, Ta₂O₅, LiTaO₃, LiNbO₃, La₂TiO₇,La₂TiO₇, SrZrO₃, ZrO₂, Y₂O₃, Nb₂O₅, La₂Ti₂O₇, LaTiO₃, HfO₂, and mixturesthereof.

In accordance with another embodiment of the method of the presentinvention, the material comprising the buffer layer is selected from thegroup consisting of transparent lithium ion permeable materials andmixed conductors. In some embodiments of the present invention, thematerial comprising the buffer layer is selected from the groupconsisting of tungsten oxides, nickel oxides, cerium oxides, molybdenumoxides, vanadium oxides, and mixtures thereof. In other embodiments ofthe present invention, the buffer layer is comprised of a materialselected from the group consisting of WO₃, NiO, CeO₂, MoO₃, V₂O₅, andmixtures thereof. In yet other embodiments, the buffer layer iscomprised of a lithium-based ceramic material including lithiumsilicates, lithium aluminum silicates, lithium aluminum borates, lithiumborates, lithium silicon oxynitrides, lithium zirconium silicates,lithium niobates, lithium borosilicates, lithium phosphosilicates,lithium nitrides, lithium aluminum fluoride, and mixtures thereof.

In accordance with another object of the present invention, a method hasbeen discovered for preparing an ion conductor layer wherein the methodcomprises the following steps: a) depositing a first ion transport layeronto a substrate, b) depositing a buffer layer onto said first iontransport layer, and c) depositing a second ion transport layer ontosaid buffer layer. The method also contemplates that the ion conductorlayer may be comprised of more than one buffer layer and more than twoion transport layers. Indeed, the ion conductor layer may be comprisedof any number of buffer and ion transport layers provided that suchlayers meet the objectives of the present invention. As such, the methodmay also comprise the steps of depositing additional ion transport andbuffer layers onto the second ion transport layer, wherein theadditional ion transport and buffer layers alternate within the ionconductor layer.

In accordance with one embodiment of the method of the currentinvention, adjacent ones of the at least two ion transport layers andbuffer layer are comprised of different materials.

In accordance with another embodiment of the method of the currentinvention, the ion transport layers are comprised of an insulatorincluding, but not limited to, silicon oxides, aluminum oxides, aluminumnitrides, niobium oxides, tantalum oxides, titanium oxides, zirconiumoxides, yttrium oxides, hafnium oxides, and mixtures thereof.

In accordance with another embodiment of the method of the currentinvention, the buffer layer is selected from the group consisting oftransparent lithium ion permeable materials and mixed conductors. Insome embodiments, the buffer layer may be selected from the groupconsisting of tungsten oxides, nickel oxides, cerium oxides, molybdenumoxides, vanadium oxides, and mixtures thereof. In other embodiments, thebuffer layer may be selected from lithium-based ceramic materials.

In accordance with another embodiment of the method of the currentinvention, the ion transport layers and/or buffer layers may beindependently deposited by means of a method selected from the groupconsisting of physical vapor deposition, intermediate frequency reactivesputtering, DC sputtering, wet chemical methods, laser ablation methods,sol-gel, metallo-organic decomposition, and magnetic sputtering.

Applicants have found that electrochromic devices utilizing the improvedion conductor layer as disclosed herein color more deeply by virtue ofthe increased voltage developed across the ion conductor prior toelectronic breakdown. Applicants have also found that electrochromicdevices utilizing the improved ion conductor layer as disclosed hereinare less susceptible to electronic leakage. Applicants have alsodiscovered that the improved ion conductor layer contained within anelectrochromic device provides thermal stabilization properties to theelectrochromic device, which are desirable for more robustmanufacturing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-section of a typical five layerelectrochromic device.

FIG. 2 is a graph of internal voltage versus current and optical densityfor a typical large area electrochromic device.

FIG. 3A is a schematic cross-section of a five layer electrochromicdevice having an improved ion conductor layer in accordance with oneembodiment of the current invention.

FIG. 3B is a schematic cross-section of a five layer electrochromicdevice having an improved ion conductor layer, wherein the counterelectrode layer and the electrochromic electrode layer are reversed.

DETAILED DESCRIPTION

One object of the present invention is to provide an electrochromicdevice having an improved ion conductor layer. The improved ionconductor layer serves to block electron flow in both directions whilepermitting ionic conduction. The improved ion conductor layer alsoprovides thermal stabilization properties, which are desirable for morerobust processing. This and other objectives are realized by means of anelectrochromic device utilizing a multi-layered thin film ion conductorcomprised of thin films of at least two ion transport layers and abuffer layer, wherein the at least two ion transport layers and thebuffer layer alternate within the ion conducting layer. Such amulti-layered thin film ion conductor layer allows for devices to colormore deeply by increasing the voltage developed across the ion conductorprior to electronic breakdown while reducing the amount of electronicleakage.

Another objective of the present invention is to provide an ionconductor layer which may be used in electrochromic devices and in otherapplications requiring ion conductor layers, such as batteries.

Yet another objective of the present invention is to provide a method ofpreparing an electrochromic device comprising an improved ion conductinglayer.

Yet a further objective of the present invention is to provide a methodof preparing an improved ion conducting layer for use in electrochromicdevices and in other applications requiring ion conductor layers.

In accordance with the present invention, FIG. 3A illustrates asolid-state electrochromic device, in cross-section, having an improvedion conductor layer. The device of FIG. 3A is similar to the solid-statedevice depicted in FIG. 1 to the extent that each of the aforementionedlayers is present in the current invention. However, the ion conductorlayer of the current invention is comprised of multiple layers, asdescribed herein. Thus, the device of the present invention, has thefollowing thin film layers: an electrochromic electrode layer (“EC”) 24acting as a first electrode which produces a change in absorption orreflection upon oxidation or reduction; an ion conductor layer (“IC”) 23comprised of alternating ion transport and buffer layers whichfunctionally replaces an electrolyte allowing the passage of ions whileblocking electronic charge; a counter electrode layer (“CE”) 22 actingas a second electrode which serves as a storage layer for ions when thedevice is in the bleached state; and two conductive layers (“TC”) 21 and25 which serve to apply an electrical potential to the electrochromicdevice. Each of the aforementioned layers are typically appliedsequentially on a substrate 26.

In operation, the electrochromic device of FIG. 3A is transformed from asubstantially transparent state to a less transparent or dark state byapplication of a positive voltage to the conductive layer 21 relative tothe other conductive layer 25. The applied voltage causes chargecompensating ions, such as lithium, sodium, or hydrogen ions, to passfrom the counter electrode layer 22 into the electrochromic electrodelayer 24 via the ion conductor layer 23. Meanwhile, electrons aretransported around the external circuit via the transparent conductors21 and 25, and injected into the electrochromic electrode layer 24. Theinjected electrons yield a reversible electrochemical reduction of thematerial comprising the electrochromic electrode layer, resulting inreversible changes in the device's intrinsic optical properties, such asoptical absorbance and the index of refraction. This overall reversibleprocess is promoted by the simultaneous injection of charge compensatingions into the electrochromic electrode layer.

In order to reverse the process for transforming the electrochromicdevice from a relatively low level of light transmission to a relativelyhigh level of light transmission, the polarity of the circuit isreversed by applying a positive voltage to the transparent conductor 25relative to the transparent conductor 21. This causes chargecompensating ions to flow out of the electrochromic electrode layer,back through the ion conductor layer 23, and into the counter electrodelayer 22. Meanwhile, the polarity reversal causes electrons to flow outof the electrochromic electrode layer, around the external circuit, andinto the counter electrode layer 22. This extraction of electrons yieldsa reversible electrochemical oxidation of the material comprising theelectrochromic electrode layer, reversing the aforementioned changes inintrinsic optical properties.

It will be appreciated that the counter electrode layer 22 and theelectrochromic electrode layer 24 may be reversed in the overallstructure of FIG. 3A. In such a reversed arrangement, as depicted inFIG. 3B, the counter electrode layer acts as the first electrode and theelectrochromic electrode layer acts as the second electrode. However, ifthe counter electrode layer and the electrochromic electrode layer arereversed, the polarity of the applied potential must be adjusted toensure that the correct polarity for the layers is maintained.

The ion conductor layer may be comprised of any number of ion transportand buffer layers provided that: (a) the ion transport and buffer layersalternate within the ion conductor layer; (b) the layer depositedimmediately adjacent to the first deposited electrode, either theelectrochromic electrode layer or the counter electrode layer, is an iontransport layer; and (c) the layer deposited immediately adjacent to thesecond deposited electrode, the other of the electrochromic electrodelayer or the counter electrode layer, is an ion transport layer. In thespecific embodiment depicted in FIG. 3A, the ion conductor layer iscomprised of two ion transport layers 31 and 33, separated by a bufferlayer 32, wherein the ion transport layers 31 and 33 are incommunication with a counter electrode layer 22 and an electrochromicelectrode layer 24, respectively. In one preferred embodiment, the ionconductor layer is comprised of two ion transport layers and one bufferlayer. In another preferred embodiment, the ion conductor layer iscomprised of three ion transport layers and two buffer layers. In yetanother preferred embodiment, the ion conductor layer is comprised offour ion transport layers and three buffer layers.

Any two adjacent ion transport and buffer layers comprising the ionconductor layer are comprised of different materials. For example, inFIG. 3A the ion transport layer 31 may be comprised of silicon dioxide,the buffer layer 32 may be comprised of tungsten oxide, and the iontransport layer 33 may be comprised of silicon dioxide. Thus, at eachion transport and buffer layer interface, a heterogeneous junction(“heterojunction”) is formed. As defined herein, a “heterojunction”, isan electronic barrier resulting from the difference in bandgap energiesof the dissimilar materials constituting adjacent layers. As such,electronic conductivity is blocked in a direction perpendicular to thelayers by virtue of this electronic bandgap difference. A heterojunctionis formed at each ion transport and buffer layer interface or eachbuffer layer and ion transport interface comprising the ion conductorlayer. Heterojunctions are also formed at the ion transport layer andfirst electrode interface and the ion transport layer and secondelectrode interface. It is believed that these heterojunctions providefor the enhanced electron blocking of the current invention.

The materials comprising the ion transport layers are selected frominsulators. When used in window applications, such as architecturalwindows, it is preferred that the ion conductor be selected from atransparent insulator. As used herein, “transparent” means that asignificant percentage of incident light intensity may be transmittedthrough a thin film over a wide angular range of incidence. Thepercentage of transmission of incident light intensity may range fromless than about 20% transmittance to greater than about 80%transmittance, depending on the specific application, with thenon-transmitted light intensity lost to physical processes includingoptical absorption, light scattering, and optical reflection. Themagnitude of light intensity loss depends upon both the thickness of theinsulator material and the insulator material's intrinsic opticalproperties, including optical absorptivity, the concentration of lightabsorbing species, the concentration and cross section of lightscattering centers, and the refractive index with respect to adjoiningmaterials. It will be appreciated that both the thickness and intrinsicoptical properties of the insulator material may be selected to suitcertain applications. For example, in architectural window applications,the percent transmission needs to be optimized but not necessarilymaximized. In this case, a significant loss of incident light intensitymay be desired. On the other hand, in certain electronic displayapplications, the light scattering and optical absorption of theinsulator material may both need to be maximized to provide asubstantially opaque backdrop for the reversibly coloring electrochromicmaterial. It can further be appreciated that the selection andcombination of ion transport layers comprised of various insulatormaterials affords several optical degrees of freedom over which opticaltransmission, reflection and light scattering can be optimized.

According to the theory of band structure in solids, the insulators ofthe current invention are characterized by a full valence band separatedfrom an empty conduction band by a few electron volts. As such,electronic conduction cannot take place in either the filled or emptybands unless additional carriers (i.e. electrons or holes) areintroduced. However, the ionic conductivity of such insulator materialsis unrelated to the band structure, depending instead on the physicalstructure of the material itself. In the case of an insulator sandwichedbetween two electrodes, and without wishing to be bound by any oneparticular theory, it is believed that the simplest electronicconduction mechanism is the direct quantum-mechanical tunneling ofelectrons or holes from a first to a second electrode. The carriers mayalso be injected into the conduction or valence band of the insulator bythermionic or Schottky emission over the metal-insulator interfacebarrier. Moreover, the carriers may tunnel through the insulator barriergap at high fields (field or cold emission).

Transport of carriers in the conduction band, however, is modulated byscattering processes. While it is believed that lattice scattering isnot expected to be significant for the thin layers of the currentinvention, it should be noted that less ordered films (such as amorphousfilms) contain a large number of traps. In the presence of such traps,conduction can also take place by tunneling between traps, or dependingon the type of traps, by hopping from trap to trap (see Kasturi L.Chopra's Thin Film Phenomena, McGraw Hill: 1969, pages 479 andfollowing, incorporated herein by reference).

Insulators which may be utilized as part of the current inventioninclude, but are not limited to, silicon oxides, aluminum oxides,aluminum nitrides, niobium oxides, tantalum oxides, titantium oxides,zirconium oxides, yttrium oxides, hafnium oxides, and mixtures thereof.Specific insulators which may be utilized include, but are not limitedto, SiO₂, Al₂O₃, Nb₂O₃, Ta₂O₅, LiTaO₃, LiNbO₃, La₂TiO₇, La₂TiO₇, SrZrO₃,ZrO₂, Y₂O₃, Nb₂O₅, La₂Ti₂O₇, LaTiO₃, HfO₂ and mixtures thereof. Specificmixtures which may be utilized include mixtures of SiO₂ and Al₂O₃ andmixtures of ZrO₂ and Y₂O₃. If a mixture of any two materials isutilized, the amount of the first material to the amount of the secondmaterial ranges from about 30:1 to 1:30, preferably from about 20:1 toabout 1:20.

In some preferred embodiments of the present invention, the materialscomprising the ion transport layers are selected from SiO₂, Al₂O₃, andNb₂O₃.

In other preferred embodiments, the ion transport layer is a mixture ofa silicon oxide and aluminum oxide, wherein the ratio of silicon oxideto aluminum oxide in such a mixture ranges from about 25:1 to about1:25, preferably the ratio of silicon oxide to aluminum oxide rangesfrom about 11:1 to about 17:1.

One skilled in the art would appreciate that any of the materialsselected for use in the ion transport layers may be mixed with one ormore additives selected from metals, metal oxides, compounds containingmetals, molecules, or atomic species to alter the chemical and/orphysical properties of one or more ion transport layers.

In some embodiments, each ion transport layer comprising the ionconductor is comprised of the same material. In other embodiments, someof the ion transport layers comprising the ion conduction may becomprised of one type of material while other ion transport layerscomprising the same ion conductor may be comprised of a different typeof material. Indeed, it is possible for each of the ion transport layerscomprising the ion conductor layer to be made from different materials.

The thickness of the ion transport layer varies depending on thematerial comprising the layer and the desired properties of theelectrochromic device. However, the ion transport layer typically rangesfrom about 1 nm to about 70 nm in thickness, preferably from about 5 nmto about 30 nm in thickness. Each ion transport layer comprising the ionconductor layer may be about the same thickness or may be of variedthicknesses. It is preferred, however, that each of the ion transportlayers be about the same thickness. Moreover, the ion transport layersmay be of the same or different thicknesses as compared with the bufferlayers.

Any material may be used as a buffer layer provided it allows for thepassage of ions from one ion transport layer to another. In someembodiments, the material comprising the buffer layer has low or noelectronic conductivity, but this is not essential. The buffer layersare selected from materials including transparent lithium ion permeablematerials and mixed conductors. As used herein, a “mixed conductor”means an ion/electron conductor. In some embodiments, the buffer layercomprises metal oxides including, but not limited to, tungsten oxides,nickel oxides, cerium oxides, molybdenum oxides, vanadium oxides, andmixtures thereof. Specific buffer layer materials include, but are notlimited to, WO₃, NiO, CeO₂, MoO₃, V₂O₅, and mixtures thereof. Specificmixtures which may be utilized include mixtures of NiO and WO₃, mixturesof CeO₂ and MoO₃, mixtures of CeO₂ and V₂O₅, mixtures of MoO₃ and V₂O₅,and mixtures of CeO₂, MoO₃, and V₂O₅. If a mixture of any two materialsis utilized, the amount of the first material to the amount of thesecond material ranges from about 30:1 to about 1:30, preferably fromabout 20:1 to about 1:20.

In other embodiments, the buffer layer comprises a silica-based, analumina-based, or an alumina-silica-based structure. Other buffermaterials particularly adapted for lithium ion transmission arelithium-based ceramic materials including lithium silicates, lithiumaluminum silicates, lithium aluminum borates, lithium borates, lithiumsilicon oxynitrides, lithium zirconium silicates, lithium niobates,lithium borosilicates, lithium phosphosilicates, lithium nitrides,lithium aluminum fluoride, and other lithium-based ceramic materials,silicas, or silicon oxides.

In preferred embodiments, the buffer layer is selected from the groupconsisting of tungsten oxide and mixtures of nickel oxide and tungstenoxide.

In some embodiments, each buffer layer comprising the ion conductorlayer is comprised of the same material. In other embodiments, however,some of the buffer layers comprising the ion conductor layer may becomprised of one type of material while other buffer layers comprisingthe same ion conductor layer may be comprised of a different type ofmaterial. Indeed, it is possible for each of the buffer layerscomprising the ion conductor to be made from different materials.

The thickness of the buffer layer varies depending on the materialcomprising the layer and the desired properties of the electrochromicelectrode layer device. However, the buffer layer typically ranges fromabout 10 nm to about 300 nm in thickness, preferably from about 30 nm toabout 150 nm in thickness. Each buffer layer comprising the ionconductor layer may be about the same thickness or may be of variedthicknesses. It is preferred, however, that the buffer layers be aboutthe same thickness. Moreover, the buffer layers may be of the same ordifferent thicknesses as compared with the ion transport layers.

In one preferred embodiment, the ion conductor layer is comprised of asilicon dioxide first ion transport layer, a tungsten oxide bufferlayer, and a second silicon dioxide ion transport layer. In anotherpreferred embodiment, the ion conductor layer is comprised of a silicondioxide first ion transport layer, a niobium oxide buffer layer, and asilicon dioxide second ion transport layer. In yet another preferredembodiment, the ion conductor layer is comprised of a siliconoxide/aluminum oxide first ion transport layer, a tungsten oxide bufferlayer, and a silicon oxide/aluminum oxide second ion transport layer. Inyet a further preferred embodiment, the ion conductor layer is comprisedof a silicon dioxide first ion transport layer, a tungsten oxide firstbuffer layer, a silicon dioxide second ion transport layer, a tungstenoxide second buffer layer, and a silicon dioxide third ion transportlayer.

The overall thickness of the ion conductor layer depends upon how manyion transport and buffer layers comprise the ion conductor layer, thematerials comprising each of those layers, and the thicknesses of eachof those layers.

The electrochromic devices of the present invention comprise a counterelectrode layer 22 in communication with one of the ion transportlayers. The purpose of the counter electrode layer is primarily to“insert” and store the charge compensating ions, such as lithium,sodium, or hydrogen ions, when not employed in the electrochromicelectrode layer. Some counterelectrode materials are also electrochromicin that they change their shade or transparency as ions move in or out.Such materials can complement the coloration of the electrochromiclayer.

The counter electrode layer 22 is typically formed from a material whichis capable of storing ions and then releasing these ions fortransmission to the electrochromic electrode layer 24 in response to anappropriate electric potential. In some embodiments, the counterelectrode layer is comprised of a metal oxide including the oxides ofvanadium, niobium, nickel, iridium, cobalt, tungsten, tantalum andmolybdenum. Preferred metal oxide materials for the counter electrodelayer include vanadium pentoxide, niobium oxide, nickel oxide, nickelhydroxide, iridium oxide, cobalt oxide, molybdenum oxide, and mixtures(both intercalated and chemically combined forms) of these materials,such as chromium vanadium oxide, tungsten-nickel oxide, tantalum-nickeloxide and the like. In some embodiments, the counter electrode layer iscomprised of a mixed metal oxide comprising a first transition metaloxide present as a stable metal oxide matrix and a second transitionmetal doped into the stable metal oxide matrix. The first transitionmetal is selected from chromium, tungsten, and tantalum. The secondtransition metal is selected from vanadium and nickel. The currentinvention also contemplates the lithium doped compounds of each of theaforementioned metal oxides.

The thickness of the counter electrode layer 22 varies depending on theapplication sought for the electrochromic device, the transmission rangedesired, and the material comprising the counter electrode layer. Assuch, the thickness may range from about 50 nm to about 650 nm. In oneembodiment of the present invention, the thickness may range from about150 nm to about 250 nm, preferably ranging from about 175 nm to about205 nm in thickness.

The electrochromic devices of the present invention also comprise anelectrochromic electrode layer 22 in communication with another of theion transport layers. The materials constituting the electrochromicelectrode layer 24 are well known in the art and include inorganicmaterials, organic materials, and/or composites of inorganic and organicelectrochemically active materials such that the electrochromicelectrode layer is capable of receiving ions transferred from the CElayer 22. Exemplary electrochemically active inorganic metal oxidesinclude WO₃, V₂O₅, MoO₃, Nb₂O₅, TiO₂, CuO, Ni₂O₃, Ir₂O₃, Cr₂O₃, Co₂O₃,Mn₂O₃, mixed oxides (e.g W—Mo oxide, W—V oxide) and the like. Othermaterials which may be utilized in the electrochromic electrode layer ofthe current invention, include those enumerated in C. G. Granvist,Handbook of Inorganic Electrochromic Materials, 1995: Elsevier,incorporated herein by reference. One skilled in the art would recognizethat each of the aforementioned metal oxides may be appropriately mixedwith metals including lithium, sodium, potassium, molybdenum, vanadium,titanium, and/or other suitable metals, compounds, or moleculescontaining metals. In one preferred embodiment, the EC layer 24 isselected from tungsten oxide or tungsten oxide doped with another metalor metal containing molecule.

The thickness of the electrochromic electrode layer 24 varies dependingon the electrochemically active material chosen. However, the EC layer24 typically ranges from about 50 nm to about 550 nm in thickness,preferably from about 300 nm to about 450 nm.

The materials employed for the conductive layers 21 and 25 are wellknown in the art. Exemplary conductive layer materials include coatingsof indium oxide, indium tin oxide, doped indium oxide, tin oxide, dopedtin oxide, zinc oxide, doped zinc oxide, ruthenium oxide, dopedruthenium oxide and the like, as well as all thin metallic coatings thatare substantially transparent, comprised of metals including gold,silver, aluminum, nickel alloy, and the like. It is also possible toemploy multiple layer coatings, such as those available from Pilkingtonunder the trade name of TEC-Glass®, or those available from PPGIndustries under the trade names SUNGATE® 300 and SUNGATE® 500. Theconductive layers 21 and 25 may also be composite conductors prepared byplacing highly conductive ceramic and metal wires or conductive layerpatterns on one of the faces of the substrate and then over coating thiswith transparent conductive materials such as indium tin oxide or dopedtin oxides. The conductive layers may be further treated withappropriate anti-reflective or protective oxide or nitride layers.

Preferably, the conductive layers utilized in the present invention aretransparent layers of indium tin oxide.

In some embodiments, the material selected for use in conductive layer25 is the same as the material selected for use in conductive layer 21.In other embodiments, the material selected for use in conductive layer25 is different than the material selected for use in conductive layer21.

Typically, the conductive layer 25 is disposed on a substrate 26 havingsuitable optical, electrical, thermal, and mechanical properties suchas, for example, glass, plastic or mirror materials, as a coating havinga thickness in the range of about 5 nm to about 10,000 nm, preferably inthe range of about 10 nm to about 1,000 nm. However, any thickness ofthe conductive layer may be employed that provides adequate conductancefor the electrochromic device and which does not appreciably interferewith the transmission of light where required. Moreover, conductivelayer 21 is typically the final layer of the electrochromic devicedeposited on the counter electrode layer 22. Other passive layers usedfor improving optical properties, or providing moisture or scratchresistance may be deposited on top of the active layers. Theseconductive layers are connected to an electrical power source in aconventional manner.

Typically, the substrate 26 of the electrochromic device is comprised oftransparent glass or plastic such as, for example, acrylic, polystyrene,polycarbonate, allyl diglycol carbonate, styrene acrylonitrilecopolymer, poly(4-methyl-1-pentene), polyester, polyamide, etc. It ispreferable for the transparent substrate 26 to be either clear or tintedsoda lime glass, preferably float glass, in which case a sodium iondiffusion barrier is typically applied to the bare substrate beforedepositing any of the layers described above. The sodium diffusionbarrier prevents sodium ions from migrating from the bulk of the glasssubstrate into the overlying films, especially the first conductivelayer and the electrochromic layer, during thermal processing. Ifplastic is employed, it is preferably abrasion protected and barrierprotected using a hard coat of, for example, a silica/siliconeanti-abrasion coating, a diamond-like protection coating or the like,such as is known in the plastic glazing art. Generally, the substrateshave a thickness in the range of about 0.01 mm to about 10 mm, andpreferably in the range from about 0.1 mm to 5 mm. However, anysubstrate of any thickness which will provide a functioningelectrochromic device may be employed.

One illustrative example of an electrochromic device employing two iontransport layers is: a bottom conductive layer, a tungsten oxideelectrochromic electrode layer, a silicon oxide first ion transportlayer, a tungsten oxide buffer layer, a second silicon oxide layer, anickel oxide counter electrode layer, and a top conductive layer.Another example of an electrochomic device having two ion transportlayers is: a bottom conductive layer, a tungsten oxide electrochromicelectrode layer, a silicon oxide first ion transport layer, a niobiumoxide buffer layer, a silicon oxide second ion transport layer, a nickeloxide counter electrode layer, and a top conductive layer. An example ofan electrochromic device having three ion transport layers is: a bottomconductive layer, a tungsten oxide electrochromic electrode layer, asilicon oxide first ion transport layer, a tungsten oxide first bufferlayer, a silicon oxide second ion transport layer, a tungsten oxidesecond buffer layer, a third silicon oxide ion transport layer, a nickeloxide counter electrode layer, and a top conductive layer.

The electrochromic device of the present invention may be powered withalternate electrical sources including solar cells, thermoelectricsources, wind generators, etc., to make them self-sustaining. These maybe also coupled into charge storage devices such as batteries,re-chargeable batteries, capacitors or other means.

The electrochromic device of the present invention may also be used asfilters in displays or monitors for reducing the ambient lightintensity, e.g., sun glare, that is incident on the monitor or displaysurface. Thus, the device may be employed to enhance the image qualityof displays and monitors, particularly in well lit conditions.

One skilled in the art would appreciate that the ion conductor layer asdescribed herein may be used in any other application or electrochromicdevice where an ion conductor layer is needed, such as in batteries.That is, the ion conductor layer is not limited to use in the specificelectrochromic device described herein.

Also provided is a method of fabricating an electrochromic device havingan improved ion conductor layer as described herein. The sequence ofdeposition steps, the number of deposition layers, and the compositionor type of layers which are deposited may be varied to achieve thedesired results without departing from the teachings of the presentinvention.

Foremost, a bottom conductive layer is deposited on a substrate. Thebottom conductive layer may be deposited by any techniques known in theart including wet chemical methods, chemical vapor deposition, orphysical vapor deposition processes. In a preferred embodiment, thematerials comprising a conductor layer are deposited via sputtering ontoa transparent substrate to form a first transparent conductor layer.

A first electrode, either an electrochromic electrode layer or a counterelectrode layer, is then deposited on the bottom transparent conductorlayer through wet chemical methods, chemical vapor deposition, orphysical vapor deposition. Preferred methods of deposition includesol-gel, spray pyrolysis, electrodeposition, metallo-organicdecomposition, laser ablation, pulsed laser ablation, evaporation,e-beam assisted evaporation, sputtering, intermediate frequency reactivesputtering, RF sputtering, magnetic sputtering, DC sputtering, reactiveDC magnetron sputtering and the like.

In preferred embodiments, the first electrode is deposited viaintermediate frequency reactive sputtering or DC sputtering techniques.In some embodiments, the first electrode layer is deposited on a heatedbottom transparent conductor layer.

The individual ion transport and buffer layers comprising the ionconductor layer are then sequentially deposited on the first depositedelectrode. Any number of ion transport and buffer layers may bedeposited on the electrochromic electrode layer provided that: a) theion transport and buffer layers alternate within the ion conductorlayer; b) the layer deposited immediately adjacent to the firstdeposited electrode, either the electrochromic electrode or the counterelectrode, is an ion transport layer; and c) the layer depositedimmediately adjacent to the second deposited electrode, the other of theelectrochromic electrode or the counter electrode, is an ion transportlayer. The ion transport and buffer layers may be comprised of thematerials discussed herein. In preferred embodiments, adjacent ones ofthe ion transport layers and buffer layer are comprised of differentmaterials.

Each ion transport layer and/or buffer layer may be deposited via thesame deposition process or may be deposited via different processes. Theindividual ion transport and buffer layers may be sequentially depositedby wet chemical methods, chemical vapor deposition or physical vapordeposition. Such methods of deposition include sol-gel, metallo-organicdecomposition, laser ablation, evaporation, e-beam assisted evaporation,sputtering, intermediate frequency reactive sputtering, RF sputtering,magnetic sputtering, DC sputtering, and the like.

In some preferred embodiments, the ion transport and buffer layers areeach independently deposited by intermediate frequency reactivesputtering or DC sputtering techniques. In other preferred embodiments,the ion transport and buffer layers are each deposited by sol-gel thinfilm deposition techniques including dip coating, spin coating and spraycoating. In yet other preferred embodiments, some of the ion transportlayers or buffers are deposited by sputtering while other ion transportor buffer layers are deposited by sol-gel techniques. The procedures fordepositing such layers by sputtering or sol-gel coating are known tothose skilled in the art.

A second electrode, the other of the electrochromic electrode layer orthe counter electrode layer, is then deposited on the bottom transparentconductor layer through wet chemical methods, chemical vapor deposition,or physical vapor deposition. Preferred methods of deposition includesol-gel techniques, spray pyrolysis, electrodeposition, metallo-organicdecomposition, laser ablation, pulsed laser ablation, evaporation,e-beam assisted evaporation, sputtering, intermediate frequency reactivesputtering, RF sputtering, magnetic sputtering, DC sputtering, reactiveDC magnetron sputtering and the like.

A second conductive layer 21 is deposited on the counter electrode layer22 by methods well known in the art and as described above in thedeposition of the first conductive layer 25.

Indeed, it is possible that all of the layers comprising theelectrochromic device are deposited via magnetron sputter deposition inthe same vacuum processing chamber so as to increase device fabricationmanufacturability, meaning that the yields are likely to be improved asa result of reduced handling, and the throughput is also likely to beincreased as a result of fewer processing steps. Moreover, depositingall of the layers in the same chamber would result in a reduction in thenumber of short circuits.

Finally, charge compensating ions such as protons (H+), lithium ions, orsodium ions, are intercalated into the electrochromic device. As usedherein, the term “intercalation” means the reversible insertion of amolecule, atom or ion into the lattice of an electrochromic devicelayer. In preferred embodiments of the current invention, the chargecompensating ion is lithium, wherein the lithium ions are deposited bymagnetron sputter deposition of atomic lithium from a metallic sputtertarget into the device, under vacuum processing conditions.

Typically, the intercalation step occurs after the deposition of one orboth of the electrode layers. However, the intercalation step may occurafter the deposition of any layer of the electrochromic device.

The amount of charge compensating ion deposited is carefully controlledsuch that an amount of charge compensating ion is added that allows forthe greatest transmission of light through the electrochromic device.

The device may optionally be heat treated by heating the electrochromicdevice. In some embodiments, the heat treatment process is carried outsubsequent to fabrication of the device, i.e. after the electrochromiclayers have been deposited and at least one of the electrochromic layerand/or counterelectrode layers has been reduced via intercalation ofcharge compensating ions, as discussed above. Carrying out the heattreatment process at this point improves the switching characteristicsof the electrochromic devices. Moreover, it is believed that the heattreatment process improves the conductivity and transparency of thedevice, especially the transparent conductor layers. Further, it isbelieved that the improved ion conductor of the current invention actsas a thermal stabilization layer which helps stabilize the integrity ofthe interfaces during any heat treatment process.

The heat treatment process may occur in a vacuum, an inert atmosphere,or an atmospheric oven. The treatment itself typically occurs attemperatures ranging from about 40° C. to about 550° C., preferablyranging from about 200° C. to about 500° C. In some embodiments, theelectrochromic device is placed in an oven at room temperature and thenheat is applied. In other embodiments, the electrochromic device isplaced in a pre-heated oven. The device may be heated for a time rangingfrom about 1 minute to about 120 minutes, preferably ranging from about10 minutes to about 30 minutes. In some embodiments, the temperature isramped as the heat treatment process progresses.

In other embodiments, the device can be heated prior to the depositionof the second transparent conductor. This method results inelectrochromic device whose properties are similar to those discussed inthe preceding embodiment, but allows for the heating to be done in thesame process chamber as the deposition, resulting in improved processflow.

As already mentioned, the position of the counter electrode layer 22 andthe electrochromic layer 24 may be reversed in the overall structurepresented in FIG. 3. One skilled in the art would appreciate that shouldthe layers be reversed, the method of manufacturing the device does notchange with regard to the steps that must be performed to generate eachlayer.

One skilled in the art would also appreciate that the methods utilizedabove to create the improved ion conductor layer of the presentinvention may be used to develop an ion conductor for use in connectionwith any electrochromic device or any other application requiring ionconductor layers, such as batteries. That is, the methods used todevelop the ion conductor layer are not limited to use in the specificelectrochromic device discussed herein. Moreover, the method of makingthe improved ion conductor discussed above may also be used to depositan improved ion conductor on any surface or substrate, including, butnot limited to, electrodes or conductive thin films.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. An electrochromic device comprising: a first electrode comprising oneof an electrochromic electrode layer and a counter electrode layer, asecond electrode comprising the other of said electrochromic electrodelayer and said counter electrode layer, an ion-conductor layer forconducting ions between said first and second electrodes comprising atleast two ion transport layers and a buffer layer, said at least two iontransport layers and said buffer layer alternating within said ionconductor layer such that said ion transport layers are in communicationwith said first and second electrodes, a first conductive layer, and asecond conductive layer, said first and second electrodes and saidion-conductor layer being sandwiched between said first and secondconductive layers.
 2. The electrochromic device of claim 1, whereinadjacent ones of said at lease two ion transport layers and said bufferlayer are comprised of different materials.
 3. The electrochromic deviceof claim 2, wherein said at least two ion transport layers are comprisedof an insulator.
 4. The electrochromic device of claim 3, wherein saidinsulator is selected from the group consisting of silicon oxides,aluminum oxides, aluminum nitrides, niobium oxides, tantalum oxides,titanium oxides, zirconium oxides, yttrium oxides, hafnium oxides, andmixtures thereof.
 5. The electrochromic device of claim 4, wherein saidinsulator is a mixture of a silicon oxide and an aluminum oxide, whereinthe amount of said silicon oxide to the amount of said aluminum oxideranges from about 25:1 to about 1:25.
 6. The electrochromic device ofclaim 5, wherein said amount of said silicon oxide to said amount ofsaid aluminum oxide ranges from about 11:1 to about 17:1.
 7. Theelectrochromic device of claim 4, wherein said insulator is a mixture ofa zirconium oxide and a yttrium oxide, wherein the amount of saidzirconium oxide to the amount of said yttrium oxide ranges from about25:1 to about 1:25.
 8. The electrochromic device of claim 4, whereinsaid insulator is mixed with an additive selected from the groupconsisting of metals and metal oxides.
 9. The electrochromic device ofclaim 3, wherein said insulator is selected from the group consisting ofSiO₂, Al2O₃, Nb₂O₃, Ta₂O₅, LiTaO₃, LiNbO₃, La₂TiO₇, La₂TiO₇, SrZrO₃,ZrO₂, Y2O₃, Nb₂O₅, La₂Ti₂O₇, LaTiO₃, HfO₂, and mixtures thereof.
 10. Theelectrochromic device of claim 2, wherein said buffer layer is comprisedof a material selected from the group consisting of transparent lithiumion permeable materials and mixed conductors.
 11. The electrochromicdevice of claim 2, wherein said buffer layer is comprised of a materialselected from the group consisting of tungsten oxides, nickel oxides,cerium oxides, molybdenum oxides, vanadium oxides, and mixtures thereof.12. The electrochromic device of claim 11, wherein said buffer layer isa mixture of a nickel oxide and a tungsten oxide, wherein the amount ofsaid nickel oxide to the amount of said tungsten oxide ranges from about25:1 to 1:25.
 13. The electrochromic device of claim 2, wherein saidbuffer layer is comprised of a material selected from the groupconsisting of WO₃, NiO, CeO₂, MoO₃, V₂O₅, and mixtures thereof.
 14. Theelectrochromic device of claim 2, wherein said buffer layer is comprisedof a lithium-based ceramic material.
 15. The electrochromic device ofclaim 14, wherein said lithium-based ceramic material is selected fromthe group consisting of lithium silicates, lithium aluminum silicates,lithium aluminum borates, lithium borates, lithium silicon oxynitrides,lithium zirconium silicates, lithium niobates, lithium borosilicates,lithium phosphosilicates, lithium nitrides, lithium aluminum fluoride,and mixtures thereof.
 16. The electrochromic device of claim 1, whereinsaid at least two ion transport layers have a thickness ranging fromabout 1 nm to about 70 nm.
 17. The electrochromic device of claim 16,wherein said thickness of said at least two ion transport layers rangesfrom about 5 nm to about 30 nm.
 18. The electrochromic device of claim1, wherein said buffer layer has a thickness ranging from about 10 nm toabout 300 nm.
 19. The electrochromic device of claim 18, wherein saidthickness of said buffer layer ranges from about 30 nm to about 150 nm.20. The electrochromic device of claim 1, wherein said electrochromicelectrode layer is comprised of a material selected from the groupconsisting of metal oxides and mixed metal oxides.
 21. Theelectrochromic device of claim 20, wherein said metal oxides areselected from the group consisting of tungsten oxides, vanadium oxides,molybdenum oxides, niobium oxides, titanium oxides, copper oxides,iridium oxides, chromium oxides, cobalt oxides, manganese oxides, andmixtures thereof.
 22. The electrochromic device of claim 1, wherein saidcounter electrode layer is comprised of a material selected from thegroup consisting of metal oxides and mixed metal oxides.
 23. Theelectrochromic device of claim 22, wherein said metal oxides areselected from the group consisting of vanadium oxides, niobium oxides,nickel oxides, nickel hydroxides, iridium oxides, copper oxides,tungsten oxides, tungsten oxides, molybdenum oxides, and mixturesthereof.
 24. The electrochromic device of claim 22, wherein said mixedmetal oxides comprise a first transition metal oxide present as a stablemetal oxide matrix and a second transition metal doped into said stablemetal oxide matrix.
 25. The electrochromic device of claim 24, whereinsaid first transition metal oxide is selected from the group consistingof chromium, tungsten, and tantalum and wherein said second transitionmetal oxide is selected from the group consisting of vanadium andnickel.
 26. The electrochromic device of claim 1, wherein said first andsecond conductive layers are comprised of a material selected from thegroup consisting of metal oxides and transparent coatings of transitionmetals.
 27. The electrochromic device of claim 1, disposed on asubstrate selected from the group consisting of glass and plastic. 28.The electrochromic device of claim 1, wherein said ion-conducting layerconducts lithium ions.
 29. An ion conductor layer for transporting ionsbetween a first electrode and a second electrode comprising at least twoion transport layers and a buffer layer, said at least two ion transportlayers and said buffer layer alternating within said ion conductor layersuch that said each of said at least two ion transport layers are incommunication with said first and second electrodes.
 30. The ionconductor layer of claim 29, wherein adjacent ones of said at least twoion transport layers and said buffer layer are comprised of differentmaterials.
 31. The ion conductor layer of claim 30, wherein said atleast two ion transport layers are comprised of an insulator.
 32. Theion conductor layer of claim 31, wherein said at least two ion transportlayers have a thickness ranging from about 1 nm to about 70 nm.
 33. Theion conductor layer of claim 30, wherein said buffer layer is comprisedof a material selected from the group consisting of transparent lithiumion permeable materials and mixed conductors.
 34. The ion conductorlayer of claim 30, wherein said buffer layer is comprised of a materialselected from the group consisting of tungsten oxides, nickel oxides,cerium oxides, molybdenum oxides, vanadium oxides, and mixtures thereof.35. The ion conductor layer of claim 30, wherein said buffer layer iscomprised of a lithium-based ceramic material.
 36. The ion conductorlayer of claim 29, wherein said insulator is selected from the groupconsisting of silicon oxides, aluminum oxides, aluminum nitrides,niobium oxides, tantalum oxides, titanium oxides, zirconium oxides,yttrium oxides, hafnium oxides, and mixtures thereof.
 37. The ionconductor layer of claim 29, wherein said lithium-based ceramic materialis selected from the group consisting of lithium silicates, lithiumaluminum silicates, lithium aluminum borates, lithium borates, lithiumsilicon oxynitrides, lithium zirconium silicates, lithium niobates,lithium borosilicates, lithium phosphosilicates, lithium nitrides,lithium aluminum fluoride, and mixtures thereof.
 38. The ion conductorlayer of claim 29, wherein said buffer layer has a thickness rangingfrom about 10 nm to about 300 nm.
 39. The ion conductor layer of claim29, wherein said ion conductor layer transports lithium ions.
 40. Anelectrochromic device comprising: a) a first electrode comprising one ofan electrochromic electrode layer and a counter electrode layer, b) asecond electrode comprising the other of said electrochromic electrodelayer and said counter electrode layer, c) an ion-conductor layer forconducting ions between said first and second electrodes comprising atleast three ion transport layers and at least two buffer layers, said atleast three ion transport layers and said at least two buffer layersalternating within said ion conductor layer such that two of said iontransport layers are in communication with said first and secondelectrodes, d) a first conductive layer, and e) a second conductivelayer, said first and second electrodes and said ion-conductor layerbeing sandwiched between said first and second conductive layers. 41.The electrochromic device of claim 40, wherein said at least three iontransport layers are comprised of an insulator.
 42. The electrochromicdevice of claim 41, wherein said insulator is selected from the groupconsisting of silicon oxides, aluminum oxides, aluminum nitrides,niobium oxides, tantalum oxides, titanium oxides, zirconium oxides,yttrium oxides, hafnium oxides, and mixtures thereof.
 43. Theelectrochromic device of claim 41, wherein said insulator is selectedfrom the group consisting of SiO₂, Al2O₃, Nb₂O₃, Ta₂O₅, LiTaO₃, LiNbO₃,La₂TiO₇, La₂TiO₇, SrZrO₃, ZrO₂, Y2O₃, Nb₂O₅, La₂Ti₂O₇, LaTiO₃, HfO₂, andmixtures thereof.
 44. The electrochromic device of claim 41, whereinsaid insulator is a mixture of a silicon oxide and an aluminum oxide,wherein the amount of said silicon oxide to the amount of said aluminumoxide ranges from about 25:1 to about 1:25.
 45. The electrochromicdevice of claim 41, wherein said insulator is a mixture of a zirconiumoxide and a yttrium oxide, wherein the amount of said zirconium oxide tothe amount of said yttrium oxide ranges from about 25:1 to about 1:25.46. The electrochromic device of claim 41, wherein said insulator ismixed with an additive selected from the group consisting of metals andmetal oxides.
 47. The electrochromic device of claim 40, wherein saidbuffer layer is comprised of a material selected from the groupconsisting of transparent lithium ion permeable materials and mixedconductors.
 48. The electrochromic device of claim 40, wherein saidbuffer layer is comprised of a material selected from the groupconsisting of tungsten oxides, nickel oxides, cerium oxides, molybdenumoxides, vanadium oxides, and mixtures thereof.
 49. The electrochromicdevice of claim 48, wherein said buffer layer is a mixture of a nickeloxide and a tungsten oxide, wherein the amount of said nickel oxide tothe amount of said tungsten oxide ranges from about 25:1 to 1:25. 50.The electrochromic device of claim 40, wherein said buffer layer iscomprised of a material selected from the group consisting of WO₃, NiO,CeO₂, MoO₃, V₂O₅, and mixtures thereof.
 51. The electrochromic device ofclaim 40, wherein said buffer layer is comprised of a lithium-basedceramic material.
 52. The electrochromic device of claim 51, whereinsaid lithium-based ceramic material is selected from the groupconsisting of lithium silicates, lithium aluminum silicates, lithiumaluminum borates, lithium borates, lithium silicon oxynitrides, lithiumzirconium silicates, lithium niobates, lithium borosilicates, lithiumphosphosilicates, lithium nitrides, lithium aluminum fluoride, andmixtures thereof.
 53. The electrochromic device of claim 40, whereinsaid buffer layer has a thickness ranging from about 10 nm to about 300nm.
 54. An electrochromic device comprising: a first electrodecomprising one of an electrochromic electrode layer and a counterelectrode layer, a) a second electrode comprising the other of saidelectrochromic electrode layer and said counter electrode layer, b) anion-conductor layer for conducting ions between said first and secondelectrodes comprising at least two ion transport layers and a bufferlayer, said at least two ion transport layers and said buffer layeralternating within said ion conductor layer such that said ion transportlayers are in communication with said first and second electrodes, saidbuffer layer comprising a mixture of a nickel oxide and a tungstenoxide, wherein the amount of said nickel oxide to the amount of saidtungsten oxide ranges from about 25:1 to about 1:25, c) a firstconductive layer, and d) a second conductive layer, said first andsecond electrodes and said ion-conductor layer being sandwiched betweensaid first and second conductive layers.
 55. An electrochromic devicecomprising: a) a first electrode comprising one of an electrochromicelectrode layer and a counter electrode layer, b) a second electrodecomprising the other of said electrochromic electrode layer and saidcounter electrode layer, c) an ion-conductor layer for conducting ionsbetween said first and second electrodes comprising at least two iontransport layers and a buffer layer, said at least two ion transportlayers and said buffer layer alternating within said ion conductor layersuch that said ion transport layers are in communication with said firstand second electrodes, said buffer layer comprising a lithium-basedceramic material; d) a first conductive layer, and e) a secondconductive layer, said first and second electrodes and saidion-conductor layer being sandwiched between said first and secondconductive layers.
 56. The electrochromic device of claim 55, whereinsaid lithium-based ceramic material is selected from the groupconsisting of lithium silicates, lithium aluminum silicates, lithiumaluminum borates, lithium borates, lithium silicon oxynitrides, lithiumzirconium silicates, lithium niobates, lithium borosilicates, lithiumphosphosilicates, lithium nitrides, lithium aluminum fluoride, andmixtures thereof.
 57. The electrochromic device of claim 55, whereinsaid buffer layer has a thickness ranging from about 10 nm to about 300nm.